Limb-Specific Modulation of Muscle Synergies and Segmental Coordination During Curved Running

Curved running imposes asymmetrical mechanical demands on the lower-limbs and thus provides a model to test the adaptability of the locomotor system. This study investigated how muscle synergies reorganise during curved versus straight-line running. Using non-negative matrix factorisation of EMG signals, four synergies were extracted from both inner and outer limbs. While the overall modular structure was preserved, spatial patterns reorganised systematically while temporal patterns showed earlier onsets, particularly in synergies associated with push-off and late swing. Adaptations were limb-specific: the inner limb displayed greater reweighting and reduced complexity, while the outer limb showed more anticipatory shifts. Higuchi’s fractal dimension indicated reduced complexity in touchdown and late swing synergies but increased complexity in push-off, suggesting differential demands for robust versus finely tuned control. To corroborate this, kinematic analyses confirmed that curved running modified intersegmental coordination, with divergence of the covariation plane between inner and outer limbs, reflecting their distinct functional roles in redirecting versus propelling the body. Together, these findings indicate that curved running use modular locomotor control strategies which combine robust rhythm-generating spinal networks with asymmetric, limb-specific modulation. This coordination likely arises from the interaction of feedforward CPG activity with feedback-driven adjustments at mechanically critical phases of the gait cycle, providing new quantitative evidence for the flexible yet stable organisation of human locomotion.